The present invention relates to a method for molding certain aromatic polyetherimides to enhance their rate of crystallization and to the compositions used in such method.
Prior to the present invention, as shown by Allan Sharpless, Introduction to Polymer Crystallization, London, Edward Arnold Publishers Ltd. (1966) pgs. 64-76, it was generally known that crystallization of certain polymers such as polyethylene could occur using various nucleating agents to modify the final orientation of physical ordering of the polymer after it was subjected to crystallization conditions. As shown by U.S. Pat. No. 4,599,396, Takekoshi et al., crystalline polyimides can be made exhibiting superior solvent resistance after being molded in various structural, decorative, and protective applications. Although the polyetherimides of Takekoshi et al. have been found to possess many desirable characteristics, their use has been somewhat restricted because they cannot be economically fabricated due to their slow crystallization rate, such as 20 minutes or more, when annealed within their optimum crystallization range.
It would be desirable, therefore, to be able to enhance the crystallization rate of polyetherimides having equilibrium melting points below 400.degree. C. to be able to produce shaped articles exhibiting a high degree of solvent resistance in a more economic manner.
The present invention is based on the discovery that polyetherimides consisting essentially of at least 30 chemically combined repeating groups of the formula, ##STR1## can be injection molded to the crystalline state in substantially less time, if the polyetherimide is blended prior to molding with an effective amount of an aromatic imide or aromatic imide oligomer, as defined hereinafter, where Q and Q.sup.1 are the same or different divalent aromatic groups having the formula, ##STR2## where J is oxygen or sulfur, and n and m are sesparately O or 1.